I think your questions are perfectly valid and really shows a sort of discrepancy in how games like, for example, Horizon Zero Dawn and Anthem are judged in a different manner.
In Traditional games, usually, there is a market pitch where the developers tell you "Hey, this is our game, these are the things there are on it right now, do you like it?" and if people like what was shown, they play all that was in the game and it was good, then cool, it was worth the money and time I spent on this, I got what they told me and it was fine. Sometimes people like it so much, the developers announce an expansion, a DLC, or even a new campaign in some games (Like Horizon and Witcher), for example. The thing is, the game is sold as a finished product.
Some games, however, are sold not only on what the game offers now, but what they will offer in the future. In the case of Anthem, Destiny, Fallout, and some MMO's, too, the game that is SOLD is not just the game you will get at launch, but the promise also contains new content that will come in a predetermined pace, and a longevity to the gameplay that will make you play between these updates. When they sell you these games, they are PROMISING you that you will get a ton more quests, items, enemies, etc. IT IS part of the package. If that promise is broken or it turns out the new stuff is really underwhelming, people are on their absolute right to complain.
In Anthems case, specifically, Bioware said time and time and time again that these things would becoming giving players new reason to keep playing the game forever (The game director actually said that). And it seems more and more that they are not going to honor their part of the bargain.